Delivering content in multiple formats

ABSTRACT

Content may be received at an edge location in one format, but delivered to a terminal on an access network in another format. The received content may be transcoded at the edge location. The transcoded content may be stored, or immediately delivered. The transcoded content may be fragmented prior to storage. Multiple copies of the transcoded content may be maintained in multiple formats. These formats may be aligned with one another such that delivery of the content can include delivering portions of the content in one format and other portions of the content in another format.

RELATED APPLICATIONS

This application is a continuation of pending U.S. patent applicationSer. No. 15/421,778, filed Feb. 1, 2017, and entitled “DeliveringContent in Multiple Formats,” which is a continuation of U.S. patentapplication Ser. No. 13/872,222, filed Apr. 29, 2013, now U.S. Pat. No.9,596,283, and entitled “Delivering Content in Multiple Formats,” whichis a continuation of U.S. patent application Ser. No. 12/894,580, filedSep. 30, 2010, now U.S. Pat. No. 8,458,362, and entitled “DeliveringContent in Multiple Formats,” the disclosures of which are incorporatedby reference herein in their entirety and made part hereof.

BACKGROUND

In traditional networks, content (e.g. a movie) is often delivered froma content source to an edge location of a distribution network, and thecontent is then delivered to end-user terminals from the edge locationvia an access network. The format of the content typically remainsunchanged as it travels between the content source and the terminals.Sometimes the content may need to be delivered in different formats inorder to accommodate varying capabilities of different types ofterminals. In such circumstances, transcoders, which may be located atthe content source, transcode the content into the different formats forthe different terminals. Thus, the same content may be sent over thedistribution network more than once in order to deliver the content inmore than one format. What is needed is an apparatus and method for moreefficient delivery of transcoded content to a terminal.

BRIEF SUMMARY

This summary is not intended to identify any critical or key elements.Instead, it merely presents certain introductory concepts. The fullscope of this disclosure may be appreciated upon reading the fullspecification and figures, of which this summary is a part.

At an edge location of a network, between a distribution network and anaccess network, one or more servers may receive content from thedistribution network, transcode the content into one or more formats,and distribute the transcoded content over the access network. The oneor more servers may also store a plurality of copies of the content,each copy encoded in a different format.

The one or more servers may begin distributing the content over theaccess network in response to receiving a request from a terminal on theaccess network. The format in which the content is distributed may beselected such that it is compatible with the terminal. This may involveidentifying whether the terminal can play or view a format and/orwhether there is sufficient bandwidth between the terminal and the oneor more servers to deliver the format.

The transcoding may be performed such that some or all of the i-framesof each copy of the content are aligned with one another. This allows aterminal to switch between formats of the content mid-viewing withoutreceiving frames that were already transmitted in another format.

The quality of the received content may be verified prior to transcodingand retransmission. Similarly, the quality of the transcoded content maybe verified. The quality of the transcoded content may be verified byensuring that some or all of the i-frames are aligned and by ensuringthat control signals of the original content appear in the transcodedcontent.

The transcoded content may be fragmented and stored such that eachfragment is randomly accessible. Each fragment may begin with an i-frameand be followed by p-frames and/or b-frames, and optionally byadditional i-frames. The transcoded content may be fragmented whether ornot the i-frames are aligned across copies of the transcoded content.Each fragment may be encapsulated in a packet, such as an IP packet, fortransport across a network.

Other embodiments and variations will be apparent upon reading thedetailed description set forth below. The disclosure is not intended tobe limited in any way by this brief summary.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example of a distribution network and an accessnetwork in accordance with one or more aspects of the disclosure.

FIG. 2 illustrates an example of an access network in accordance withone or more aspects of the disclosure.

FIG. 3 illustrates an example of a server in accordance with one or moreaspects of the disclosure.

FIG. 4 shows an illustrative method of receiving and distributingcontent in accordance with one or more aspects of the disclosure.

FIG. 5 shows an illustrative method of transmitting content in differentformats in accordance with one or more aspects of the disclosure.

FIG. 6 illustrates three sample streams in which groups of pictures arealigned in accordance with one or more aspects of the disclosure.

DETAILED DESCRIPTION

FIG. 1 illustrates an example of a distribution network 151-154, anaccess network 161 and 162, and servers 100 a and 100 b at a locationbetween the distribution and access networks (e.g., an edge location).In this example, the distribution network 151-154 links content source150 with one or more servers 100 a and one or more servers 100 b.Although servers 100 a may be made up of more than one server, they willbe referred to as server 100 a for simplicity. Similarly, one or moreservers 100 b will be referred to as server 100 b. Content, such asdata, a video, and/or an audio program, may be sent from content source150 via satellite uplink 151. Content source 150 may be a centralizedrepository of pre-existing video and/or audio programs. It may also bethe location at which a live video stream or other content is created,such as the video feed from a live football game. The content from thecontent source 150 is transmitted in an initial, or first format. In theillustrative example of FIG. 1, this initial or first format is labeled“Format 1.”

As seen in the example of FIG. 1, the content may be relayed in thefirst format by satellite 152 to receiver 153. In this example, receiver153 is connected via communication link 154 to server 100 a and server100 b. A short-range wired or wireless connection, or any other type ofconnection, including long-range connections, may be used. Thedistribution network may contain more than one content source. Thecontent sources may be collocated, or they may also reside in a varietyof locations. The content from each source may be in the same format, orthe content from some or all of the sources may be in different formats.Similarly, if a content source transmits more than one piece of content,each piece of content may be in a different format.

While the example distribution network 151-154 shown in FIG. 1 includesa satellite, a variety of other network technologies may also be used todeliver content to the edge of the distribution network. Another exampleof a distribution network is a network that connects a content sourcewith one or more servers located at an edge of an access network usingfiber optic, coaxial cable, Ethernet, wireless connections, or the like,including a hybrid mix of connections. Networks that combine varioustransmission technologies to deliver content to the edge of adistribution network may be used. Similarly, various content sources maybe connected to a server in different ways. For instance content source150 is illustrated as being connected to servers 100 a and 100 b viasatellite 152 and also via physical link 154, but another content sourcemay be connected to sever 100 a and/or 100 b via only physical links ofone or more types.

Server 100 a, like server 100 b, may receive content sent from contentsource 150. Servers 100 a and 100 b may be called edge servers, as theyare located at the edge of the distribution network, which may be alarge distance from content source 150 and receiver 153. The edgeservers may store and/or transmit the content in the format in which itwas received. For instance, memory 104 b of server 100 b includes thecontent in Format 1, and the content may be sent to terminal 173 fromserver 100 b in Format 1.

An example of a format is 1920×1080 pixels per screen, 30 frames persecond, progressive scan (noninterlaced) video using the H.264 codec(also known as AVC or MPEG-4 Part 10) accompanied by 5.1 channel soundencoded according to the Dolby Digital AC-3 standard. A large variety offormats exist, and more are being developed. Different pieces of contentmay be received in different formats. Other formats may use otherresolutions, frame rates, interlacing techniques, video codecs, audiocodecs, and number of audio channels. They may also vary in the amountof compression (or bit rate) applied to the source content, the audiosampling frequency, the closed captioning or subtitling standards used,the presence and type of active format descriptions used, etc. Examplesof other video codecs include, for example, Widows Media 9 and MPEG-2.Examples of other audio codecs include, for example, MP3, ACC, and PCM.

A variety of different terminals may be connected to the edge serversvia an access network, such as networks 161 and 162. Examples ofterminals include display devices, set-top boxes, cable cards in a cablenetwork, personal computers, and other units having a processor and/ormemory. Some terminals may support a different set of encoding formatsthan other terminals. In some cases, there may not be a common encodingformat that is supported by all of the terminals on the access networkor within a user's premises. In other cases, the terminals may allsupport a common encoding format, but only some of them may supportnewer or otherwise more preferred encoding formats. Similarly, thereceived content may be in a format other than the preferred oruniversally supported encoding format. Thus, for a variety of reasons itmay be desirable or even required that the edge servers transcode thereceived content from a first format to a second format usingtranscoders 101. The edge servers may store and/or transmit the contentin the second format. For example, memory 104 b of server 100 b may alsostore the content in Format 2, and the content may be sent to terminals174 and 175 in Format 2.

The received content may also be trancoded to a third format, which islabeled Format 3 in FIG. 1. The content may be stored for laterdistribution in memory 104 a in this format, and it may be transmittedto terminal 170 in this format. As depicted in memories 104 a and 104 bof FIG. 1, the received content may or may not be stored in its originalformat (Format 1) after it is transcoded.

Transmissions of the transcoded content may occur according to aschedule or they may occur in real time as the content is received. Theymay also occur in response to a request from a terminal. For example,Terminal 171 may request a specific item of content be delivered. Anexample of such a request is a video on demand request. Content requesthandler 103 a receives this request and may respond by having thecontent sent to Terminal 171 in Format 2. The content request handler103 a may select Format 2 because the request identified that thecontent is to be delivered in Format 2. Alternatively, content requesthandler 103 a may select Format 2 because, for example, it was the mostappropriate format in which to send the content given knowledge of thecapabilities of Terminal 171, because it is the default format, or for avariety of other reasons, as will be discussed in more detail below.

The received content may be transcoded immediately after it is received,but it may also be stored and transcoded later, such as when a requestfor that content is received from a terminal, or when a transmission isscheduled to take place. By transcoding at a later time, the storagerequired by an edge server may be reduced because only one copy of thecontent is stored. Transcoding content multiple times, however,potentially increases power consumption and/or processor load.

In some embodiments, the transcoded content may be transmitted toterminals on the access network as well as stored at an edge location,such as in memory 104 a of server 100 a. In such embodiments, the samecontent may not be transcoded to the same format repeatedly. Instead ofrepeatedly transcoding, a copy of the transcoded content may be storedafter the first transcoding. The stored copy, which is alreadytranscoded, may be transmitted in response to a subsequent request forthe same content encoded in the same format.

In another embodiment, content may be transcoded to some or all of theavailable formats prior to the time the content is requested by aterminal or made available for request. Such an embodiment maydistribute over time the processor load required for transcoding. It mayalso reduce the required processing power by allowing the transcoding tooccur slower than real-time. Combinations of the above examples may alsobe used. For instance, an edge server may transcode the content to someformats, such as popular formats, prior to a demand for the content, butit may not transcode the content to all supported formats prior to ademand. Thus, some formats, such as less common formats, may betranscoded only upon demand, thereby balancing storage space againstprocessor load.

The various streams (or other types of transmissions, which may bedelivered using any protocol, including, for example, IP) of contentreceived by an edge server may be encoded according to the same codec,or the codec may vary from stream-to-stream. Regardless of what formatthe content is received in, the above methods of storing, transmitting,and/or transcoding the received content may be used. The same methoddoes not need to be used for each piece of received content. Forinstance, it may be useful to transcode some content, such as popularcontent, prior to first distribution, but to not transcode othercontent, such as more esoteric content, until a request is received forthat content to be delivered in a format other than the format in whichthe content was received.

The edge servers may include probes, such as probes 102 a and 102 b,which may comprise hardware and/or software elements that verify thatthe transcoders output what they were expected to output. For example,in the case of video content, the probes may ensure that the each of theformats of the content output from the transcoder are aligned such thatthe format used to transmit the content to a terminal may be changed inthe middle of the content without retransmitting any frames. Probes mayalso be used to verify the quality of the received content, andpotentially to trigger a request for retransmission of the receivedcontent if the quality is not as expected. The verification operationsperformed by probes, such as probes 102 a and 102 b, will be discussedin further detail below.

As seen in FIG. 1, terminals 170-172 are connected to server 100 a viaaccess network 161. Terminals 173-175 are connected to server 100 b viaaccess network 162. Access networks 161 and 162 may be of various types.Examples of types of access networks include, but are not limited to,passive optical networks (PON), digital subscriber lines (DSL), widearea wireless networks of various types, and hybrid fiber coaxial cable(HFC) networks. An access network may utilize known media accesscontrol, transport, and other communication protocols used with aparticular type of access network architecture and communicationtechnology. Like a distribution network, an access network may includevarious nodes, and it may combine various technologies for transmittingdata.

Access networks may support a large number of terminals, such fifty, onehundred, one thousand, or more terminals. Access networks may span manymiles, and they may even span hundreds or thousands of miles.

Servers 100 a and 100 b may be connected to a distinct set of terminals,as in the illustrative example shown in FIG. 1. However, this need notnecessarily be the case. For example, in a mobile (e.g. cellular)network example implementation, a terminal may be movable, and thus itmay receive signals from either or both of servers 100 a and 100 b,depending on its present geographic location.

FIG. 2 illustrates another example of an access network. In thisexample, edge servers, such as server 100 a of FIG. 1, include a varietyof ports, such as ports 121 a-e. These ports may each be connected to aplurality of terminals via a physical connection. In a cable networkexample implementation, the edge servers may be located at a centraloffice (e.g. a headend), and each of their communications ports mayserve a group of terminals that all receive the same set of signals fromserver 100 a. The group of terminals may share the same communicationlink. As illustrated in the access network of FIG. 2, homes 201-208(which may be residences, businesses, institutions, etc.) each tap intocommunication link 200 of the access network, which is connected to port121 a. Each home may include one or more terminals, such as a televisionset top box, a cable-card, or another device capable of receiving thecontent transmitted on line 200 of the access network. As seen in FIG.2, homes 211-219 tap into communication line 210 of the access network,which is connected to port 121 b. Thus, the terminals in homes 211-219each receive the signals that are transmitted on line 210 of the accessnetwork.

Although in this example each of ports 121 serves a unique group ofterminals, this is not necessarily the case in other examples. Forinstance, communications port 121 may be a single port, and the signalssent from communication port 121 may be forwarded to various portions ofthe access network by other hardware. For instance, in a hybrid fibercoax (HFC) network example implementation, the output of port 121 may besent to a separate cable modem termination system (CMTS) or a convergedmulti-service access platform (CMAP) for distribution to homes 201-208and/or 211-219. Other appropriate hardware may be used to forward theoutput of port(s) 121 to the terminals in the example of a fiber opticnetwork. In the example of a mobile (e.g. cellular) network, the outputof port(s) 121 may be forwarded to appropriate cell towers of the accessnetwork such that the signals destined for each terminal will reach thelocation of that terminal.

FIG. 3 illustrates an example of a server of the type that may be usedat the edge of the distribution network. Server 100 includes processingunit 110 and at least one communications port 120, which may beconnected to one or more distribution networks. Server 100 also includesat least one communications port 121, which may be connected to anaccess network as described previously. The content sent and receivedfrom communications ports 120 and 121 may be communicated to processingunit(s) 110 via input/output hardware 125. This hardware may includecommunications controllers, modulators, demodulators, and the like.Communications ports 120 and 121 may send and/or receive information viaany type of coaxial cable, Ethernet cable, fiber optic cable, wirelesssignal transmission, etc. Examples of wireless signal transmissionsinclude transmissions to or from satellites as well as transmissions toor from cellular radios. The input/output hardware and/or software 125may also include a variety of interface units and drives for reading,writing, displaying, and/or printing data or files.

Processing unit(s) 110 may include one or more processors. At least someof the processors execute instructions 131, which may be stored in amemory 104. Memory 104 may include RAM 113, ROM 115, and/or other typesof data storage, such as a sequentially accessed data storage medium.Memory 104 may store executable instructions 131, such as instructionsfor transcoding content, handling content requests, verifying the resultof a transcoding operation, and/or various other operations describedherein. Memory 104 may also include other data 132. Examples of otherdata include event logs, performance statistics, information aboutsubscribers, including the types of terminals used by subscribers, audioand/or video content, etc.

Some or all of executable instructions 131 and/or other data 132 mayoptionally be stored in a database format, such as database 132′.Databases may be internal to server 100, or they may be otherwiseaccessible to server 100. For example, a database may be stored in aseparate database server or servers. Local copies of some or all of thedatabases may be stored by the memory 104 of the server 100. Informationcan be stored in a single database, or separated into different logical,virtual, or physical databases, depending on system design.

Those of skill in the art will appreciate that the functionality ofserver 100 may be spread across multiple physical devices, for example,to distribute processing load or to increase modularity. For example,some or all of the input/output hardware 125 may reside in a separatephysical unit from some or all of the processing unit(s) 110 and/or someor all of the memories 104. In other words, the functional blockdivision as shown in FIG. 3 may either correspond to or be independentof the physical implementation of the functional blocks.

One or more aspects of the present disclosure may be embodied incomputer-usable or readable data and/or executable instructions, such asin one or more program modules, executed by one or more processors orother devices as described herein. Generally, program modules includeroutines, programs, objects, components, data structures, etc. thatperform particular tasks or implement particular abstract data typeswhen executed by a processor in a computer or other device. The modulesmay be written in a source code programming language that issubsequently compiled for execution, or may be written in a scriptinglanguage such as (but not limited to) HTML or XML. The computerexecutable instructions may be stored on a computer readable medium,such as a hard disk, optical disk, removable storage media, solid statememory, RAM, etc. As will be appreciated by one of skill in the art, thefunctionality of the program modules may be combined or distributed asdesired in various embodiments. In addition, the functionality may beembodied in whole or in part in firmware or hardware equivalents such asintegrated circuits, field programmable gate arrays (FPGA), and thelike. Particular data structures may be used to more effectivelyimplement one or more aspects of the present disclosure, and such datastructures are contemplated within the scope of executable instructionsand computer-usable data described herein.

FIG. 4 shows an illustrative method of receiving and distributingcontent. In step 401, content is received from a distribution network,or another source, in a first format. In step 402, that content isstored. As noted above, step 402 is optional, as the content may bestored only in a transcoded format, or the content may never be storedin any format. In step 403, the received content is verified. Step 403may be completed at any time, including prior to step 402 and while thecontent is being received in step 401. Step 403 is also optional.

The content may be verified in a variety of different ways. For example,it may be verified to determine if any errors were introduced duringtransport over the distribution network. This may be accomplished, forexample, by calculating a checksum for the content that was received andcomparing the calculated checksum to the checksum received with thecontent. It may also be accomplished, for example, by detecting videojitter or other video artifacts. The content may be rejected if anyerrors were introduced. Alternatively, a threshold quality level orrequirement may be tested for. For instance, if errors, such asexcessive jitter, occur only infrequently, then the content may beaccepted, but if errors occur frequently, then the content may berejected.

If the content is rejected, a retransmission from the distributionnetwork may be required.

Where feasible, the retransmission may be obtained from a differentsource on the distribution network. In some situations, rejecting thecontent may not be feasible and/or desirable. Thus, it is also possiblethat content that does not meet quality requirements will not berejected.

Whether the content is rejected or not, compliance or lack of compliancewith quality requirements, including the frequency and type of anyerrors, may be logged and reported. Such logging may also be desirableeven in the case where retransmission is able to solve any qualityproblems and/or where no problems were detected at all. Logging mayoccur at the location where the error is detected, and it may also occurat other locations. For instance, it may be desirable to report errorsto a central database, which may store quality reports received frommultiple locations. A quality log, whether stored locally or in acentral database, may allow for the reported events to be inspectedand/or visualized in a number of different formats, including graphicalsummaries. A user may wish to manually override default behavior basedon such data or based on other information. For example, a user mayinstruct a server, such as server 100 a, to ignore a detected qualityproblem or to request retransmission when it otherwise would not. Suchinstructions may allow for fine-tuning of a server's performance.

In step 404, the content is transcoded to a second format. As discussedabove, the transcoding may occur at the time the content is received. Itmay also occur later, such as at a time system resources allow fortranscoding to take place or when the content is first requested in aformat that is not already stored. As part of the transcoding process,metadata associated with the content may also be updated. For example,if the received content was encoded at 30 frames per second, but is wastranscoded to only 15 frames per second, the metadata associated withthe transcoded content may be modified to indicate 15 frames per secondinstead of 30.

In step 405, the content is optionally stored in the second format. Instep 406, the transcoded content may be verified, similar to step 403above. Additional details regarding how transcoded content may beverified are discussed below. In step 408, the content may betransmitted, via an access network for example, in an appropriateformat. This step may be responsive to receiving a request for thecontent in step 407. An appropriate format may be either of the first orsecond formats in the present example.

In the case where content may be transmitted in more than one format, anedge server may store pre-determined knowledge of what formats arecompatible with and should be used for each terminal. This knowledge maybe obtained from an external source, or it may be obtained from theterminals themselves (e.g. automatically or through user input). Forexample, the terminals may request the content in a particular format.Terminals may also provide a list of formats in which the content may bedelivered. This list may or may not be organized to show that someformats are more preferred than others. Terminals may also provide listsof supported and/or preferred formats independent of a request forcontent, such as in response to a poll or as part of a setup and/orconfiguration process.

Reasons beyond compatibility may also dictate which format to use whentransmitting content. For instance, some terminals may be associatedwith users or subscribers whose service plan allows for higher qualityvideo or audio than other users or subscribers. Similarly, someterminals may be connected to speakers and/or displays that are notcapable of taking advantage of certain formats. For instance, a terminalconnected to only two speakers may not gain anything by receiving sixchannels of audio. Thus, bandwidth on the access network can be savedand distinctions between service plans can be adhered to by deliveringcontent to different terminals in different formats.

Another consideration when selecting a format in which to transmitcontent is the user's experience. For instance, network congestion orother errors may cause higher bandwidth formats to display incorrectlyor to be delivered too slowly to allow for real-time display. Thus alower-bandwidth format may be preferred. However, the network congestionmay be temporary, and after the condition clears a higher-bandwidthformat may be preferred due the greater amount of information in thehigher-bandwidth format. Thus, it may be desirable to begin deliveringcontent to a terminal in one format, but to change that format to alower or higher bandwidth format in response to the conditions of thelink between an edge server, or another device in the system, and theterminal. Multiple changes may occur during transmission of a singlepiece of content in response to varying conditions on the link. Thebandwidth required of some formats may change over time. For example,video content may require more bandwidth during fast action scenes thanslower-paced scenes. It may be the case that the bandwidth requiredduring these fast action scenes exceeds the capacity of the link betweenthe edge server and the terminal. Thus, changes in format may occurduring transmission even if the bandwidth on the link does not change.

FIG. 5 shows an illustrative method of transmitting content in differentformats. In step 501, the highest bit rate supported or allocated by thelink is identified. Alternatively, the current capacity of a link thatmay be congested is determined. The link may include, for example, theaccess network between edge server and the terminal. In addition toconsidering the link, the capabilities of the terminal, the equipmentconnected thereto, and/or a user's subscription plan or status may alsobe considered, as discussed above. In step 502, the highest qualityformat that does not exceed the maximum supported bitrate or capacitydetermined in step 501 is selected. In step 503, the selected format maybe transmitted. Thus, the process may start by sending the highestquality format via a stream or another type of transmission that theterminal and link can support. The content in the selected format may betransmitted using a variety of protocols, including, for example, IP.Alternatively, the process may start by sending a stream in a random orpredetermined format.

In step 504, an edge server determines if errors due to lack of capacityare occurring. An error threshold may be established in order to avoidlowering the quality of the format that is transmitted due to momentaryinterference. If a lack of capacity is detected, a lower quality formatmay be selected in step 506. A lack of capacity may be a lack ofbandwidth. It may also be an inability of a terminal to process thecurrently selected format. The lower quality format selected in step 506may be the next lower quality format of the formats that are available.Alternatively, if the link speed has been determined, the lower qualityformat may be selected based on the bit rate that the link can currentlysupport, similar to step 502, above.

If it is determined in step 505 that a higher quality format would besupported, then a higher quality format is selected in step 507. Whethera higher quality format would be supported may be determined bymeasuring the link speed and/or the capabilities of the terminal. It mayalso be determined by measuring the current error rate. (If there are noor very few errors, then a higher quality format may be used.) As withstep 506, the next higher quality format may be selected. Alternatively,the format may be selected based on the bit rate supported by the link.A delay may be built into the process to avoid unnecessarily changingformats. In other words, the answer to step 504 or 505 may always be“no” unless a certain amount of time has passed. This delay may apply toincreasing the quality of the selected format, but not to decreasing thequality of the selected format.

In steps 506 and 507, if a higher or lower quality format is notavailable, then the currently selected format may be maintained. In thecase where the lowest quality format is experiencing too many errors,the transmission may cease.

Where the format used to transmit the content may change over time, asdescribed above, it may be desirable to deliver the content such thatthe changes in format are not noticeable by a user consuming thecontent. To facilitate this, is may be desirable to perform theencoding/transcoding of the content into the various formats such thatswitching between the formats does not require excessive overhead, suchas retransmission of video frames that were already transmitted inanother format.

Many video codecs organize the compressed video into i-frames, b-frames,and p-frames. An i-frame, also known as an intra-coded frame, is a fullyspecified picture. A p-frame, also known as a predicted frame, containsonly the changes in the image from a previous frame or frames. Using ap-frame instead of an i-frame may save space, resulting in a morecompressed video stream. A b-frame, also known as a bi-predictive frame,may be even more compressible, as it contains only changes in the imagefrom previous frame(s) and from subsequent frame(s). In some codecs,slices or macroblocks are used to sub-divide the picture, and eachsubdivided section may be an i, b, or p slice or block.

A video stream, for example, may be subdivided into groups of pictures.(Pictures within a video stream are also known as frames.) Such groupsbegin with an i-frame. The initial i-frame may be followed by i-, b-,and/or p-frames. Where the groups of pictures in an encoded stream arekept at a constant size, such as 15 frames, then an i-frame isguaranteed to occur ever 15 frames (at the beginning of each new groupof pictures). I-frames may occur more frequently if the groups ofpictures happen to include i-frames in subsequent positions as well asin the initial position of the group.

Where the received content is transcoded into multiple formats,switching between the formats can be accomplished withoutre-transmission of any frames if transcoding is performed such that thegroups of pictures in the different formats are aligned. When the groupsof pictures are aligned, each group of pictures begins at the same pointin the content and thus contains the same portion of the originalcontent.

FIG. 6 illustrates three sample streams labeled as stream 610, stream620, and stream 630, each having a different format. Each stream has 7frames per group of pictures, as can be seen by the fact that an i-frameoccurs every seventh frame, as seen at time t₀, t₁, t₂, t₃, and t₄. Thegroups of pictures are identified by braces 611-615, 621-625, and631-635. As seen by frame 639, it is possible but not required for agroup of pictures to contain an i-frame in a position other than thefirst position.

Streams 610, 620, and 630 are aligned such that any of the three streamsmay be selected for transmission at each of times t₀, t₁, t₂, t₃, t₄,and t₅. For example, group 611 of stream 610 could be sent from time t₀to t₁, at which point group 622 of stream 620 could be sent betweentimes t₁ and t₂, at which point group of frames 633 of stream 630 couldbe sent, etc.

With the groups of pictures aligned, re-transmission of frames can beavoided by switching formats immediately prior to the beginning of eachgroup of pictures. In the example shown in FIG. 6, switching formats attimes t₀, t₁, t₂, t₃, t₄, and t₅ avoids the need to retransmit anyframes because the first frame transmitted after each of those times isan i-frame, which, by definition, does not rely on any previous frames.

One way of achieving alignment is setting a common, constant group ofpictures size for each format, ensuring that the same starting frame isused across all formats, and ensuring that no frames are added ordropped during the transcoding process.

It may be advantageous to verify that alignment was in fact achievedafter transcoding has occurred. This may be accomplished by ensuringthat each copy of the content has the same duration, and by ensuringthat i-frames occur at the same time point in each copy of the content.If it is known that i-frames are not inserted in the middle of a groupof pictures, then one way of achieving this is by verifying thati-frames occur at consistent intervals across each copy of the content.For example, it may be verified that each copy contains one i-frameevery two seconds. If it is known that i-frames are not inserted in themiddle of a group of pictures, that the size of a group of pictures doesnot vary within any copy of the content, and that the frame rate is thesame across each copy, then verifying alignment may also be achieved bycounting the number of i-frames in each copy of the content and ensuringthat the count is the same for each copy.

Further, it may be advantageous to ensure that control signals,including extended data service signals, from the original stream aremaintained in each of the transcoded streams. For example, the originalstream may have contained an SCTE-35 signal, which is an example of asignal that indicates that an advertisement may be inserted. SCTE standsfor Society of Cable and Telecommunications Engineers. If the signal wasnot maintained during the transcoding, the signal may be inserted intothe transcoded stream. This may be accomplished by extracting thecontrol signals from the original stream and re-multiplexing thetranscoded stream such that it includes the extracted signals at thesame or approximately the same time point as the original stream. Thetime point at which to insert the extracted signal may be identified by,for example, extracting the time stamp of the location at which thesignal was inserted in the original stream. The time point may also becalculated by evaluating a presentation time included in the extractedsignal and inserting the signal immediately before or shortly before thepresentation time. The time point may also be calculated by evaluatingthe relative frame rate between the original and transcoded copies andusing the relative frame rate to identify a frame or frames at which thesignal should be inserted in the transcoded stream based on the frame orframes at which it was inserted in the original stream.

As described above, the process of transcoding to multiple streams anddelivering all or a portion of those streams to the access network mayoccur at the edge of the network on an edge server, such as server 100.However, portions of this process may also occur at other locations. Forexample, the process of transcoding to multiple formats may occur at acentralized location, such as at the content source, instead of at theedge of the distribution network. In this case, the transcoded contentmay be received by an edge server and stored at the edge of the networkfor later delivery to the access network. Instead, or in addition, thetranscoded content may be stored at the content source and transmittedon demand from the content source. The process of verifying that thesetranscoded streams have aligned groups of pictures and/or have allcontrol signals in place may be performed at the location of thetranscoder, but it may also be performed in other locations. Forexample, if the transcoding occurs at a content source, the verificationmay occur at the content source, at any point along the distributionnetwork, at the edge of the network, at any point along the accessnetwork, and/or at the terminal.

Whether the transcoding or initial encoding occurs at a content sourceor at the edge of a network, the encoded content may be fragmented intoindividual groups of pictures prior to storage. When transmitting over apacket network, such as an IP network, the payload of each packet may bepre-formed prior to transmission. For example, each group of picturesmay be transmitted in a single IP packet. Using this format, thepre-formed IP packet of a stream in any one format may be followed bythe pre-formed IP packet of a stream in another format withoutre-transmitting or dropping any frames of the content.

The transcoded streams may also be fragmented into more than one groupof pictures. These larger fragments, like the smaller fragmentsdiscussed above, may each be sent using a single IP packet. For example,a single fragment may consist of groups 631, 632, and 633 of stream 630,and these groups of frames may be contained in a single packet.Alternatively, the fragments may be split into multiple IP packets fordelivery.

Saving the encoded file or stream in fragments may be advantageous wherethe fragments are randomly accessible. This means that the beginning ofeach fragment can be located on a storage medium without having to readany of the other fragments. This may be advantageous where atransmission of a stream begins in the middle of the stream instead ofat the beginning of the stream. For example, if a stream in a formatthat has a high bit rate is being delivered, but a lower bit rate formatneeds to be delivered for the next group of pictures because of networkcongestion, the process of locating the next group of pictures in thenew lower bit rate stream is more efficient when the next group ofpictures can be randomly accessed.

A combination of random and sequential access may be used. For example,if fragments contain multiple groups of pictures, then the fragment maybe accessed directly, but the contents of the fragment may then have tobe scanned sequentially until the desired group of pictures is locatedwithin the fragment.

Random access can be achieved by maintaining an index of fragments tolocations. This index may identify the fragments sequentially, by theframe number that begins or ends the fragment, by the time within thecontent when the fragment occurs, etc. This index may be part of a filesystem. For example, each fragment may be stored as a separate file.Alternatively, the fragments may be stored in a database. Neither ofthese examples is necessary, however. Even if the stream is saved as asingle file, it may be randomly accessed if an index indicates wherewithin the file each fragment begins. For example, an index may indicateat which byte of the file each fragment begins.

The process of fragmenting may be separated from the process ofencoding. For example, an encoded stream may be sent to both afragmenter and to another receiver of the encoded stream for which thefragmentation is not useful. An example of another receiver to which theencoded stream may be sent is a mobile digital television broadcaster. Amobile digital television broadcaster may transmit the stream in yetanother format, such as ATSC-MH, which stands for advanced televisionsystems committee mobile handheld.

The process of encoding or transcoding may occur at one location, andthe process of fragmenting the stream may occur at another location. Forexample, the encoding or transcoding may occur at a content source, butthe fragmenting may occur at the edge of a network. Similarly, thefragments may be sent to an encryption or another security device, suchas a digital rights management (DRM) packager, before and/or after beingstored, and the security device may be at a separate location than theencoder and/or fragmenter. A security device, such as a DRM packager,may encrypt or otherwise restrict access of the contents of thefragments to avoid unauthorized copies of the content from being made.

While the present disclosure has described specific examples includingpresently preferred modes of carrying out the invention, those skilledin the art will appreciate that there are numerous variations andpermutations of the above described systems and techniques that fallwithin the spirit and scope of the invention as set forth in theappended claims.

What is claimed is:
 1. A method comprising: sending, by a computingdevice and via a connection, a first video stream of a content item,wherein the first video stream comprises a first plurality of fragmentsassociated with a first format; determining, by the computing device andbased on one or more characteristics of the connection, to send a secondvideo stream of the content item, wherein the second video streamcomprises a second plurality of fragments associated with a secondformat; aligning, by the computing device, and based on a first timeassociated with the first plurality of fragments and a second timeassociated with the second plurality of fragments, a first fragment ofthe first plurality of fragments and a second fragment of the secondplurality of fragments; and sending, by the computing device, after thealigning, and via the connection, the second video stream.
 2. The methodof claim 1, wherein the one or more characteristics comprise anavailable bandwidth of the connection, and wherein the determining tosend the second video stream comprises determining, based on theavailable bandwidth failing to satisfy a threshold, to send the secondvideo stream.
 3. The method of claim 1, wherein the sending the secondvideo stream comprises: ceasing, after sending the first fragment,sending of the first video stream; and sending, beginning with thealigned second fragment, the second video stream.
 4. The method of claim1, wherein the first format comprises a first resolution, and whereinthe second format comprises a second resolution.
 5. The method of claim1, wherein the first fragment comprises a first group of pictures basedon the first format, wherein the second fragment comprises a secondgroup of pictures based on the second format, and wherein the aligningfurther comprises: setting a same group of pictures size for the firstgroup of pictures and the second group of pictures, and avoiding anaddition or loss of video frames of the first video stream and thesecond video stream.
 6. The method of claim 1, further comprising:determining an index of fragments comprising the first plurality offragments and the second plurality of fragments, wherein the indexidentifies each of the fragments sequentially based on: a frame numberthat begins the fragment, a frame number that ends the fragment, or atime within the first video stream when the fragment occurs.
 7. Themethod of claim 1, wherein the aligning comprises aligning, in time withan initial I-frame of the second fragment, an initial I-frame of thefirst fragment in time with an initial I-frame of the second fragment.8. The method of claim 1, further comprising: verifying, based ondetermining that the first fragment comprises a same number of I-framesas the second fragment, the aligning.
 9. A method comprising: receiving,by a computing device and from a client device, a request for a contentitem; generating, by the computing device and according to a firstformat, a first video stream corresponding to the content item, whereinthe first video stream comprises a first plurality of fragments;generating, by the computing device and according to a second format, asecond video stream corresponding to the content item, wherein thesecond video stream comprises a second plurality of fragments; sending,by the computing device and based on the request, the first videostream; and sending, by the computing device and based on anincompatibility between the client device and the first video stream,the second video stream, wherein a first fragment of the first pluralityof fragments is aligned with a second fragment of the second pluralityof fragments.
 10. The method of claim 9, wherein the incompatibilitycomprises an insufficient bandwidth for the first video stream.
 11. Themethod of claim 9, wherein the sending the second video streamcomprises: ceasing, after sending the first fragment, sending of thefirst video stream; and sending, beginning with the aligned secondfragment, the second video stream.
 12. The method of claim 9, whereinthe first format comprises a first resolution, and wherein the secondformat comprises a second resolution.
 13. The method of claim 9, whereinthe first fragment comprises a first group of pictures based on thefirst format, wherein the second fragment comprises a second group ofpictures based on the second format, and further comprising: aligningthe first fragment with the second fragment by: setting a same group ofpictures size for the first group of pictures and the second group ofpictures, and avoiding an addition or loss of video frames of the firstvideo stream and the second video stream.
 14. The method of claim 9,further comprising: determining an index of fragments comprising thefirst plurality of fragments and the second plurality of fragments,wherein the index identifies each of the fragments sequentially basedon: a frame number that begins the fragment, a frame number that endsthe fragment, or a time within the first video stream when the fragmentoccurs.
 15. The method of claim 9, wherein an initial I-frame of thefirst fragment is aligned in time with an initial I-frame of the secondfragment.
 16. The method of claim 9, further comprising: verifying,based on determining that the first fragment comprises a same number ofI-frames as the second fragment, that the first fragment is aligned withthe second fragment.
 17. A method comprising: receiving, by a computingdevice and from a client device, a request for a content item; sending,by a computing device and to the client device, a first video stream ofa content item, wherein the first video stream comprises a firstplurality of fragments associated with a first format; transcoding, bythe computing device and based on determining an insufficient bandwidthfor the first video stream, the content item to create a second videostream, wherein the second video stream comprises a second plurality offragments associated with a second format; aligning, by the computingdevice, and based on a first time associated with the first plurality offragments and a second time associated with the second plurality offragments, a first fragment of the first plurality of fragments and asecond fragment of the second plurality of fragments; and causing, bythe computing device and after the aligning, sending of the second videostream to the client device.
 18. The method of claim 17, wherein thesending the second video stream comprises: ceasing, after sending thefirst fragment, sending of the first video stream; and sending,beginning with the aligned second fragment, the second video stream. 19.The method of claim 17, wherein the first fragment comprises a firstgroup of pictures based on the first format, wherein the second fragmentcomprises a second group of pictures based on the second format, andwherein the aligning the second fragment in time with the first fragmentfurther comprises: setting a same group of pictures size for the firstgroup of pictures and the second group of pictures, and avoiding anaddition or loss of video frames of the first video stream and thesecond video stream.
 20. The method of claim 17, wherein the aligningcomprises aligning, in time with an initial I-frame of the secondfragment, an initial I-frame of the first fragment.